Amp Power Question
Printed From: Speakerplans.com
Category: General
Forum Name: Newbie Discussion
Forum Description: Newbie Discussion/Questions. Look less stupid here...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=107138
Printed Date: 18 April 2024 at 5:58am
Software Version: Web Wiz Forums 12.06 - https://www.webwizforums.com
Topic: Amp Power Question
Posted By: sam012
Subject: Amp Power Question
Date Posted: 10 June 2022 at 1:06am
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I'm debating buying 2 x QSC RMX 4050a but a bit confused on the specs Running 4 x Void V12 1000 1) Do I run the amps in bridged @ 2600W 8ohm 2) Do I run 1 cab per channel @ 1400W 4ohm Or is it the same thing? I know I'm missing fundamental knowledge here, just trying to piece it all together The reason i'm debating buying the amps above is because they can be bought online without the agro of finding used e.g. a used k10 The reason i'm buying those drivers is for the same reason, they seem to be reasonably available to buy new
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Replies:
Posted By: Conanski
Date Posted: 10 June 2022 at 4:08am
| Are the drivers 4 ohm or 8ohm? I'd vote for 1 per channel if they are 4ohm. |
Posted By: sam012
Date Posted: 10 June 2022 at 10:43am
| 8ohm drivers |
Posted By: opus jody
Date Posted: 10 June 2022 at 11:22am
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Hi Sam. For PA work, you will almost always be wiring bass cones in parallel. If you have 4 x 8ohm cones, = 2 pairs, then You have 2 x 4ohm loads (cones) to drive, with one standard 2ch amp, not bridged. 4ohms, That's what the load is. No switches or buttons on the amp can change that. one cone= 8ohm load. 2 cones = 4 ohms 4 cones = 2 ohms, but this is a HEAVY load, and many amps will overheat & crap out with 4 cones per channel, or will not last as long. So you just need a single 2 channel 4 ohm capable amp (which is pretty much any of them), and with 2 cones on each channel, in parallel (whether its 2 single cabs linked, or a double cab)  As you only need one amp, you can spend double, and get a really good one  If you get one that's capable of driving 2 ohms, then it'll be running at half what it's capable of, so will be really happy, run cooler, and be much more reliable, plus of course, you can always add another cone or two to each channel in the future, or if one amp channel were to fail, you'd be able to wire all 4 cones on to one channel to get you through the gig. (gonna get shot down here, lol) Bridging: Setting the amp for bridge mode links the 2 channels in the amp, so that the 2 channels have one, much higher output, but it can typically only drive 8ohm = one driver. It's basically a cheap trick to turn a low power 2ch amplifier into one higher output channel, or a way of getting ridiculous wattages into a particularly high power single cone / sub (like in car audio), and I've yet to hear a bridged anp that sounds as good as 'normal' 2ch mode. I've 'fixed' numerous sound systems, just by un-bridging the amps, and wiring them properly, with a pretty standard 'Wow, what did you do? kind of response. Don't bother. ------------- Improvised Hardware Music http://vimeo.com/user9389813/videos |
Posted By: Conanski
Date Posted: 10 June 2022 at 4:29pm
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sam012 wrote:Posted By: fatfreddiescat
Date Posted: 10 June 2022 at 6:45pm
| Not sure what your paying for the RMX's but could look at an FFA, save a lot of lugging, those RMX's make my back heart just looking at them. |
Posted By: sam012
Date Posted: 10 June 2022 at 7:48pm
Which amp in particular? The QSC is £1200 inc vat online, but I agree with their weight they'd be a nightmare
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Posted By: Father-Francis
Date Posted: 10 June 2022 at 8:04pm
Look around you’l Find good amps for good prices, with FFA if I were you , I’d buy used and send it to Dave for a full physical before taking it out . https://www.ebay.co.uk/itm/195045663229?hash=item2d69a0a1fd:g:BlIAAOSwH8xie~ZU&amdata=enc%3AAQAHAAABABxXDdt4mmUHA%2FGePDKi%2FMYuvdVjA%2F19%2FEQjEy34srkDyWfDkA%2B9kxgKZqWHX7II9UxHokoBsTkwP7jbOMBZHTDri4xhWQRZLSznsvHQ3SLJazRMxvbF6eiFr1Wm1qi2oiX7%2FxxCpvxXcTESYsmElS366bMJbMmhPG%2Bfi4XOhCbkBfH7NaO%2BgsSqS9Mj7JPy3CDq78Yfew3Y5w%2BtdyEHUleOZLuaUg6aumu%2BkhoXS3SwLjDf4gz9fvMzHwLjLRzSsR3tV7MZXjJXH3uyZuA7pcdS5nbt8MeOY%2B8F%2F36oLj90ggYGK2ugpJW97Hbk0oAaXYRIcRybouBy8irINN748Yg%3D%7Ctkp%3ABFBMjpTM76lg" rel="nofollow - https://www.ebay.co.uk/itm/195045663229?hash=item2d69a0a1fd:g:BlIAAOSwH8xie~ZU&amdata=enc%3AAQAHAAABABxXDdt4mmUHA%2FGePDKi%2FMYuvdVjA%2F19%2FEQjEy34srkDyWfDkA%2B9kxgKZqWHX7II9UxHokoBsTkwP7jbOMBZHTDri4xhWQRZLSznsvHQ3SLJazRMxvbF6eiFr1Wm1qi2oiX7%2FxxCpvxXcTESYsmElS366bMJbMmhPG%2Bfi4XOhCbkBfH7NaO%2BgsSqS9Mj7JPy3CDq78Yfew3Y5w%2BtdyEHUleOZLuaUg6aumu%2BkhoXS3SwLjDf4gz9fvMzHwLjLRzSsR3tV7MZXjJXH3uyZuA7pcdS5nbt8MeOY%2B8F%2F36oLj90ggYGK2ugpJW97Hbk0oAaXYRIcRybouBy8irINN748Yg%3D%7Ctkp%3ABFBMjpTM76lg ------------- Music is the strongest form of magic.(+45 31879997)blakmanpro@gmail.com, foa@sweetboxaudio.dk |
Posted By: sam012
Date Posted: 10 June 2022 at 8:15pm
1/3rd of the weight and x2 the power for £600 more* 4050a is 2 x 1400 4r FFA-6004 is 4 x 1500w 4r
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Posted By: toastyghost
Date Posted: 10 June 2022 at 9:15pm
wweeeeeeellllll  the thing is the Watts aren’t what you’d really want more of. The peak voltage capability is what makes the speaker move and handle the peaks for dynamic, good music. Bridging was / is a way to get an amplifier to be able to handle the exceptional peak voltage demands for unclipped music transients.The AES75-20222 (M-Noise) peak SPL testing standard has a good example; a loudspeaker with an 8-ohm nominal impedance and AES power rating of 200W covering the midrange (anything above 500Hz) needs 400V of unclipped peak voltage swing to avoid being limited by amplifier capability when playing most music signals.  A Crest Factor of 10 is equivalent to 20dB from RMS to peak. These numbers aren't just plucked out of thin air either. They're the result of analysing a lot of music files and live concerts. |
Posted By: opus jody
Date Posted: 10 June 2022 at 11:16pm
Just keeping it simple. ;) ------------- Improvised Hardware Music http://vimeo.com/user9389813/videos |
Posted By: Randy Bohannon
Date Posted: 12 June 2022 at 6:22am
I’m trying to work this all out so please bear with me if my questions are silly. Isn’t it same thing to talk about power and voltage in this context? Given that speaker impedance is a constant, x volts equals y watts doesn’t it or have I missed something? A crest factor of 20dB on 200w average… that’s 20k isn’t it?! |
Posted By: opus jody
Date Posted: 12 June 2022 at 9:55am
IDK the answer, but speaker impedence isn't actually constant, it's frequency dependent. ------------- Improvised Hardware Music http://vimeo.com/user9389813/videos |
Posted By: Randy Bohannon
Date Posted: 12 June 2022 at 10:45am
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What I meant was that when comparing power delivered into a speaker, impedance is a constant. At whatever frequency, providing you are using the speaker and the same box, the load presented to the amplifier is the same. |
Posted By: snowflake
Date Posted: 12 June 2022 at 1:48pm
isn't a music signal crest factor of ~10db on the POWER of the signal not the voltage. this seems to say so under 'test signals' section where they talk about a 12dB crest factor on power https://www.danleysoundlabs.com/loudspeaker-spl-expectations-and-reality/#:~:text=The%20crest%20factor%20is%20basically,400%20watts%20for%20the%20peaks." rel="nofollow - Loudspeaker SPL Expectations and Reality | Danley Sound Labs this suggests a range of 6dB-20dB on power - but surely 20dB is on stuff like classical recordings not rock or dance music https://www.prosoundweb.com/understanding-the-nuances-of-crest-factor/" rel="nofollow - Understanding The Nuances Of Crest Factor - ProSoundWeb |
Posted By: toastyghost
Date Posted: 12 June 2022 at 10:14pm
No it isn’t. The electrical impedance changes with the acoustical load, including temperature increase and other non-linear behaviours of the transducer and cabinet. Regardless of this; you also need to consider the difference between apparent power and real power. This is super important since loudspeaker power ratings are calculated from the measured voltage and nominal (or lowest) impedance in the passband - depending on the testing standard used. 20dB crest factor is also very prominent in popular music, at the high frequencies. I suggest reading the AES75-2002 standard document and the papers related to the M-Noise test signal. |
Posted By: sam012
Date Posted: 14 June 2022 at 12:34am
The Blue Aran Jam amps are £1250 for the K16, I understand there's difference in quality between K16 + FFA6004 but my inexperience fails me completely in which would be better at this price point. The JAM amps haven't cropped up as being problematic from my googling? Would running 8ohm @ 1600w not be better than FFA which is 4 ohm @ 1500w? To answer my own question after some thought, the only benefit really is the extra ~100W of headroom for £700 less but opting for a chinese made amp (numbers below) over picking say a FFA 6004 The main amp picking issue I'm having is seeing anecdotal comments saying stuff like the "k10 sounds bad imo, the k20 is better" so I sort of have ADHD on which amp to finally decide on - as the search goes on the budget goes up and up, bringing me back to maybe I should just get the cheaper JAM amp K16 £1250: 4 channel mode: 8 ohm: 4 x 1600W 4 ohm: 4 x 2800W 2 ohm: 4 x 3500W Soundgear Saturn 16 £1080: 8ohm: 4 x 2100w 4ohm: 4 x 4200w FFA - 6004 ~£1800 ebay - 8ohm: 4 x 900W 4 Ohm 4 x 1500W |
Posted By: VECTORDJ
Date Posted: 14 June 2022 at 4:24am
| QSC Amps are A+ |
Posted By: KDW32
Date Posted: 14 June 2022 at 8:28am
I couldnt find any info on a void V12 1000 did you mean 18 or have I missed so something googling?
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Posted By: Randy Bohannon
Date Posted: 14 June 2022 at 4:42pm
Thanks for taking the time to explain it further. :) The impedance load that a particular speaker presents, in a particular box and assuming the same programme material is a constant if all that is being varied is the amplifier(s) testing it, surely? Thanks you for the references, I couldn’t track down a public domain copy of that paper but read up on The idea behind the M tone and it makes sense to me. The ran a few tracks through a spectral analyser and can see how they arrived at their conclusions. The 20 dB crest factor you mentioned makes more sense l, being primarily a function of high frequency content, as the average power content of this portion of the musical spectrum is lot lower in power than than the lower frequencies. So, if I have understood correctly, if the average programme rms if the woofer is 200w, the tweeter might be getting 10w and the 20dB crest factor on 10w seems more realistic. Why does that mean quoting power in voltage, which is independent of impedance and voice coil/cabinet reactance, is that preferable to power, which accounts for impedance by factoring in current, or indeed VA and phase which would be needed to calculate real AC power?
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